Roads seldom flood for any great distance, as the water runs down to fill the low spots. In dips, the water can be quite deep, so it is a good idea to test the depth with a stick first to make sure that you’ll be able to get through. Standing water, even when it is shallow can cause aquaplaning. Water under trees and in other areas of shade will be the last to dry.
The assumption that the good grip of modern tyres means you are always safe on wet roads in a dangerous fallacy. Driving in the rain is always hazardous, but the dangers are not just related to skidding. Lack of visibility can create dangerous situations leading to sudden accidents.
Loss of visibility in heavy rain can be worse than in fog, to such an extent that drivers sometimes can’t see at all in a really torrential downpour. Even if the wipers and demisters can keep the windscreen clear, it is often impossible to see through the thick blanket of rain around you.
If conditions are as bad as this, then it is too dangerous to carry on. If there is so much traffic that you can’t leave a large enough gap between you and the vehicle in front, or if you’re pressurized by the vehicle behind into travelling more quickly than you’d like, the answer is to get off the road and stop.
Spray from heavy vehicles is a particular problem on motorways and trunk roads, where the large road surface area collects a lot of water and drains slowly because of its lack of camber. It’s best to hang back out of the spray until the vehicle causing it moves over to the inner lane, or until the gradient gives better drainage.
In heavy rain, steer well clear of vehicles with their rear fog lamps on. The rain diffuses the strong red light, making it very difficult to see the car’s brake lights when they come on, as well as possibly having a dangerous mesmerizing effect. Despite advertizing campaigns, many drivers still use these lights wrongly; they should only be used where visibility is impaired by fog, snow or sleet.
Wet weather grip
A wheel simply rolling along the road in a straight line is in no risk of skidding or sliding, whatever the condition of the surface. Only when you try to change its speed or direction can grip be lost. How easily this can happen depends on the amount of grip available in the first place.
Many country roads offer more grip in wet weather than heavily trafficked ones in town, even though rural roads may harbour more standing water. Mud and wet leaves are very slippery, but at least you can often see them and slow down before you reach them, and take care with braking and steering while you are on them.
On roads that have begun to dry out, remember that the road will remain slippery for longer under trees and other areas of shade.